1. Field of the Invention
The present invention relates generally to data processing, and more particularly, to a system and method for enhancing error correction capability by using error information obtained in demodulation procedures.
2. Background of the Invention
In a signal processing system, data to be transmitted is modulated and coded, and data to be received is demodulated and decoded. A digital data recording/reproducing system modulates, multiplexes and codes data so as to record the data in a recording medium, and demultiplexes, demodulates and decodes the coded data so as to reproduce the recorded data. A recording/reproducing medium such as a digital video disc (“DVD”) or a compact disc (“CD”) is subject to various types of distortion, noise and interference. Various errors may occur at the output of the recording/reproducing medium. To reproduce data recorded on a disc, a laser beam is used to scan a recording surface of the disc, detect the light reflected from the recording surface of the disc, and produce a reproduction signal, for example, a radio frequency (“RF”) signal. The reproduction signal is input to a demodulation circuit where demodulation is performed. The demodulated data are sent to an error correction code (“ECC”) circuit or cyclic redundancy check (“CRC”) circuit, which is generally used to overcome errors arising from the storage medium.
As an example of an ECC circuit, an ECC decoder of the ECC circuit may process the demodulated data according to a C1/C2 convolution Reed Solomon decoding algorithm (CIRCplus). There are two kinds of error data, an erasure error and a general error. An erasure error refers to error data of which error location can be determined by an associated error flag. A general error refers to error data provided without any error flag, thereby making it possible to determine its error location. Generally, the ECC decoder corrects the general error in the C2 code, and corrects the general error and the erasure error in the C1 code.
In a conventional demodulation procedure, a reproduction signal may be sampled and quantized into a digital bit stream. A demultiplexer determines timing slots of the digital bit stream and converts the digital bit stream into modulation codes. A demodulator converts the modulation codes into symbols and sends the symbols to an ECC circuit for error correction. The ECC circuit may perform a syndrome check to determine whether the symbols contain an error, and corrects the error, if any. The ECC circuit, however, may not be able to correct the error. In the conventional demodulation procedure, some information related to the modulation codes is neglected, for example, temporal error information or spatial error information. The error information may be useful to improve error correction capability of an ECC circuit. It is thus desirable to collect error information during generation of a modulation code in a demodulation procedure.